There exists in the prior art methods and apparatus for exercising the rotary torso muscles of the human body. See for example applicant's U.S. Pat. No. 4,456,245 issued Jun. 26, 1984. Such methods and apparatus however fail to effectively isolate the rotary torso muscles from other muscles which are therefore free to combine with the torso muscles in the exercise, such that the exercise is rendered inefficient and/or inaccurate insofar as directed to the rotary torso muscles per se. Although such prior method seeks to essentially isolate the rotary torso muscles by restricting movement of the upper and lower torso, there is no provision for positively preventing movement of the upper and lower torso. Consequently the rotary torso muscles are not sufficiently isolated from other muscles to enable true measurement of the strength of the rotary torso muscles per se.